An example of an internal combustion engine that is provided with two crankshafts is proposed in JP-A-62-107238, wherein each crankshaft is linked to a piston via connecting rods. This internal combustion engine will be described with reference to FIGS. 11 and 12 hereof.
In an engine 200 as shown in FIG. 11, a first crankshaft 201 and a second crankshaft 202 are positioned horizontally and in parallel. The first crankshaft 201 is connected to a first piston 206 by a first connecting rod 203, and the second crankshaft 202 is connected to a second piston 207 by a second connecting rod 204. A first cylinder 211 and a second cylinder 212 are positioned so that the cylinder axes are perpendicular to the first crankshaft 201 and the second crankshaft 202. The first piston 206 and the second piston 207 are movably disposed within the first cylinder 211 and the second cylinder 212, respectively.
As shown in FIG. 12, the first crankshaft 201 and the second crankshaft 202 are connected via a synchronizing device 221 for inducing synchronized rotation. The synchronizing device 221 is composed of: a first drive-gear 225 that is attached to the first crankshaft 201; a second drive-gear 226 that is attached to the second crankshaft 202; and a driven-gear 227 that engages the first drive-gear 225 and the second drive-gear 226. The driven-gear 227 is attached to an output axle 228.
The first connecting rod 203 and the second connecting rod 204 slant towards the cylinder axes of the first cylinder 211 and the second cylinder 212 when the first crankshaft 201 and the second crankshaft 202 rotate in FIG. 11. The first piston 206 and the second piston 207 are pushed against the cylinder walls of the first cylinder 211 and the second cylinder 212 due to thrust-generated on the first piston 206 and the second piston 207, resulting in increased resistance to sliding, noise generation, and the like.
The distance between the first crankshaft 201 and the second crankshaft 202 in FIGS. 11 and 12 is theoretically reduced when a smaller, more compact engine 200 is designed, but since the first drive-gear 225 and the second drive-gear 226 have prescribed diameters, the distance between the first crankshaft 201 and the second crankshaft 202 only shortens to the combined length of the radius of the first drive-gear 225 and the radius of the second drive-gear 226, at a minimum.
Accordingly, a smaller, more compact internal combustion engine wherein thrust does not act on the pistons has been needed.